Abstract
The Tarim basin, a typical superimposed basin, has undergone multiple tectonic deformations. Based on abundant seismic, logging, and outcrop data, distribution characteristics of major unconformities in the basin are revealed and the tectonic-stratigraphic sequences are divided. Finally, the multiphase superposition and deformation of prototype basins are illustrated. Eight basin scale angular unconformities and 20 subordinate minor angular unconformities can be recognized. Based on these unconformities, eight tectonostratigraphic units of different protobasins formed in various tectonic settings have been classified. Arrangement and distribution of the tectonostratigraphic units determined the fundamental characteristics of tectonostratigraphy of the Tarim basin. Tectonostratigraphic units I to II recorded the evolution of the basin from continental rift or aulacogen (Sinian), passive continental margin and intracratonic depression (Cambrian to Early–Middle Ordovician), to foreland or retroarc foreland setting and depression (Late Ordovician to Silurian). Tectonostratigraphic unit III comprises large-scale terrigenous clastic depositional wedges progradated from the north to south in the southeastern slope of the basin, which indicates the continuously shallowing and uplifting along the northern basin margin. Tectonostratigraphic unit IV is a tectonic cycle from weak extension (Late Devonian) to compression (Triassic). Widely distributed mafic volcanic rocks of Carboniferous–Permian suggest an extensive setting, which was likely in relation to backarc extension. During Late Permian to Triassic, the tectonic setting of the basin changed to compression, indicated by the formation of the unconformity Tg along the Tabei uplift belt. From Triassic, the Tarim basin evolved into the period of intracontinental depressions and marginal foreland basins and experienced several cycles (tectonostratigraphic units V to VII) from rapid subsidence to strong uplift and deformation, resulting in superimposition and reformation of differently orientated protobasins filled with a series of regional depositional cycles bounded by major unconformities and consisting of extremely thick of alluvial and lacustrine deposits.
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